Here, a structural bearing is meant to be such bearings that generally are provided in buildings to bear the building or parts thereof. Especially, these are bearings falling within the rules of the European Norm EN 1337. That is, they can be components that allow rotations between two building parts and transmit loads defined in the relevant requirements and prevent displacements (fixed bearings) or allow displacements in one direction (guided bearings) or in all directions of a plane (free bearings).
The most common structural bearings are set forth in part 1 of EN 1337 in its currently valid version from 2004 (EN 1337-1:2004) in table 1. However, further designs and variations can be found in other norms. So, in EN 15129 specifically bearings for earthquake isolation are standardized. Here, the present invention particularly relates also to sliding bearings of different shapes such as for example spherical sliding bearings or the sliding isolation pendulum bearings etc. mentioned in EN 15129 and used there for earthquake isolation.
Here, a sliding element is meant to be such parts of a structural bearing that ensure and allow, respectively, a sliding movement between the parts of the structural bearing. Especially, these are parts falling within the rules of part 2 of EN 1337 in the version from 2004 (EN 1337-2:2004).
However, unlike determined in EN 1337-2:2004 the invention not only concerns structural bearings having a sliding element made of a polytetrafluoroethylene (PTFE, trade name Teflon), but generally also other polymeric plastics, in particular thermoplastics such as for example ultrahigh molecular weight polyethylene (UHMWPE), polyamide (PA), and mixtures thereof.
Basically, the demands on the polymeric plastics used as sliding material are known. On the one hand, they should allow an even distribution and transmission of the load acting on the structural bearing. On the other hand, they have to absorb sliding movements in the structural bearing (translatory and/or rotatory movements) such that—at least in the state of use—the building is not damaged. As far as that goes, the sliding movements can be realized with application-specified demands on the friction coefficient. For example, EN 1337-2:2004 defines such demands on the friction coefficient, however only for sliding parts made of PTFE. In EN 15129, in particular in section 8.3, in turn there are defined general test set-ups for the determination of friction for dissipation during an earthquake, that is such that apply for so-called seismic bearings. Further, of course such a sliding material should be resistant to environmental influences such as for example temperature, moisture, but also aggressive media such as acid rain or air pollution and have the greatest possible resistance to wear.
Experience has shown that polymeric plastics have differently pronounced properties, so that they can be selected in view of the use in such a structural bearing only by entering into various compromises between the corresponding requirements profiles.
A particularly good compromise of a particularly load-bearing, wear-resistant sliding material that is also resistant to environmental influences the applicant obtained with its MSM® sliding material. This is used in the form of sliding elements that are formed as flat and/or curved sliding discs, but also as guides. Particularly successful is the use in the field of sliding bearings, for example in so-called spherical sliding bearings, but also for seismic isolation in sliding isolation pendulum bearings. Here, the MSM sliding material has virtually led to a revolution in the construction of structural bearings, since it has led to a significantly longer durability of the bearings at lower manufacturing costs.
However, despite these excellent properties it has been shown that these already very widespread structural bearings in certain fields of application, especially in hot regions, reach the limit of their capacity. This is because in the polymeric plastics that are so far common in the construction of structural bearings (such as for example PTFE, UHMWPE) just the compression stability at higher temperatures decreases and the friction number or friction coefficient, respectively, change with an increasing temperature. As far as that goes, the energy dissipation in case of an unlubricated use under certain circumstances is not satisfactory. Moreover, the bearings with the known sliding materials in general have large dimensions, if the bearings should have a defined degree of friction to dissipate energy.